What fraction of a second do you require your signal to be given
in? What is the rate of the vibrator of your electric bell? Suppose
you have settled that point, and that the short time during which the
current is required to rise is called t; then the apparent resistance
at time t after the current is turned on is given by the formula:
R_{t} = R x e^{(R/L)t} + ( e^{(R/L)t} - 1 )
TIME CONSTANTS OF ELECTROMAGNETS.
I may here refer to some determinations made by M. Vaschy,[1]
respecting the coefficients of self-induction of the electromagnets of
a number of pieces of telegraphic apparatus. Of these I must only
quote one result, which is very significant. It relates to the
electromagnet of a Morse receiver of the pattern habitually used on
the French telegraph lines.
L, in quadrants.
Bobbins, separately, without iron cores. 0.233 and 0.265
Bobbins, separately, with iron cores. 1.65 and 1.71
Bobbins, with cores joined by yoke,
coils in series 6.37
Bobbins, with armature resting on poles. 10.68
[Footnote 1: "Bulletin de la Societe Internationale des Electriciens,"
1886.
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